Orbital mixing in few-layer graphene and non-Abelian Berry phase

TL;DR

This paper investigates how orbital mixing in few-layer graphene under magnetic fields is governed by a non-Abelian Berry phase, affecting the evolution of zero-mode Landau levels and many-body ground states.

Contribution

It reveals that orbital level mixing in PZM levels is driven by a non-Abelian Berry phase arising from degeneracy and interactions, providing new insights into Landau level evolution.

Findings

Orbital mixing avoids level crossing via a non-Abelian Berry phase.

The evolution of many-body ground states is influenced by external bias in bilayer graphene.

PZM levels exhibit sensitivity to interactions and external perturbations.

Abstract

In a magnetic field few-layer graphene supports, at the lowest Landau level, a multiplet of zero-mode levels nearly degenerate in orbitals as well as in spins and valleys. Those pseudo-zero-mode (PZM) levels are generally sensitive to interactions and external perturbations, and have a crossing among themselves or with other higher Landau levels when an external field is swept over a certain range. A close study is made of how such PZM levels evolve when they are gradually brought from empty to filled levels under many-body interactions. It is pointed out that the level spectra generally avoid a crossing via orbital level mixing and that orbital mixing is governed by a non-Abelian Berry phase that derives from an approximate degeneracy and interactions. A look is also taken into evolution/crossing of many-body ground states with increasing external bias in bilayer graphene.